Technical Reference; Principles Of Operation; Process Variables - Siemens SITRANS LR560 Operating Instructions Manual

Technical reference

A.1 Technical reference
A.2

Principles of operation

SITRANS LR560 is a 2-wire, 78 GHz FMCW (Frequency Modulated Continuous Wave)
radar level transmitter for continuous monitoring of solids and liquids in vessels to a range of
100 m (329 ft)
distance to a material surface.
FMCW radar transmits a continuous wave. The frequency of the wave is constantly
increasing: this is known as the sweep. By the time the first part of the wave has been
reflected off the target and returned to the device, the part of the wave that is just being
emitted is at a higher frequency. The difference in frequency between the transmitted and
received signals is proportional to time of flight.
Electromagnetic wave propagation is virtually unaffected by temperature or pressure
changes, or by changes in the vapor levels inside a vessel. Electromagnetic waves are not
attenuated by dust.
SITRANS LR560 consists of an enclosed electronic circuit coupled to an antenna and
process connection. The electronic circuit generates a radar signal (78 GHz) that is directed
to the lens antenna.
The signal is emitted from the lens antenna, and the reflected echoes are digitally converted
to an echo profile. The profile is analyzed to determine the distance from the sensor
reference point
calculating the display of material level and mA output.
The microwave output level is significantly less than that emitted from cellular phones.
1)
See Dimension drawings (Page 155)
2)
A.3

Process variables

The Process Variables are sensor value and measured value. Sensor value is the distance
from the sensor reference point (flange face) to the material surface. The measured value
can be either Level (distance from low calibration point to material surface), Distance
(distance from sensor reference point to the material surface), or Space (distance from high
calibration point to the material surface).
LR560 (PROFIBUS PA)
Operating Instructions, 06/2018, A5E34648471-AE
. Radar level measurement uses the time of flight principle to determine
1)
to the material surface. This value (sensor value) is used as a basis for
2)
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